Nuclear spin conversion in molecules induced by hyperfine interactions

In this paper the role of hyperfine interactions in molecular ortho-para conversion is considered. The main experimental results in the CHEF spin conversion are briefly described. The general theory of nuclear spin conversion in molecules based on intramolecular ortho-para state mixing is given. Two types of ortho-para state mixing are taken into account: the spin-spin interaction between molecular nuclei and the spin-rotation interaction. The level-crossing spectra for the spin conversion in (CH3F)-C-13 and (CH3F)-C-12 molecules are calculated for an electric field range of 0-10(4) V/cm. The spin conversion spectrum, discussed here, is an example of a new type of Doppler-free spectroscopy.